wireless: regulatory: fix channel disabling race condition

When a full scan 2.4 and 5 GHz scan is scheduled, but then the 2.4 GHz
part of the scan disables a 5.2 GHz channel due to, e.g. receiving
country or frequency information, that 5.2 GHz channel might already
be in the list of channels to scan next. Then, when the driver checks
if it should do a passive scan, that will return false and attempt an
active scan. This is not only wrong but can also lead to the iwlwifi
device firmware crashing since it checks regulatory as well.

Fix this by not setting the channel flags to just disabled but rather
OR'ing in the disabled flag. That way, even if the race happens, the
channel will be scanned passively which is still (mostly) correct.

Cc: stable@vger.kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/wireless/reg.c b/net/wireless/reg.c
index e6df52dc8c6972a6c418f5fed9111e040b0e35b4..cc35fbaa45787ddeba99c0ea67ed4c5e317e7dd0 100644 (file)
--- a/net/wireless/reg.c
+++ b/net/wireless/reg.c
@@ -855,7 +855,7 @@ static void handle_channel(struct wiphy *wiphy,
                        return;
 
                REG_DBG_PRINT("Disabling freq %d MHz\n", chan->center_freq);
-               chan->flags = IEEE80211_CHAN_DISABLED;
+               chan->flags |= IEEE80211_CHAN_DISABLED;
                return;
        }